The present invention relates to lubricants and lubricant additives.
A lubricant is a substance capable of reducing friction, heat, and wear when introduced as a film between solid surfaces. Generally, lubrication is provided between solid surfaces to prevent contact between the surfaces, thereby reducing friction, wear, or both. The type of lubrication required for a particular application depends on a variety of factors, including the degree of motion between the surfaces.
Boundary lubricants are employed to physically or chemically treat surfaces in solid-to-solid surface contact that are at rest or at low relative speeds with respect to one another. Boundary lubricants generally undergo a controlled chemical reaction or physical interaction with one or both contact surfaces to form protective stationary films that discourage contact (and, hence, wear) therebetween.
Elastohydrodynamic lubrication, by contrast, lubricates surfaces that are in motion at high relative velocities. For example, two surfaces in rolling contact with high relative velocities create an increase in pressure at the points of contact. Lubricant viscosity is related to pressure exponentially and this large increase in pressure due to the rolling greatly increases the viscosity of the lubricant. In elastohydrodynamic lubrication, the increased viscosity creates a thin film that prevents contact between the surfaces. Elastohydrodynamic lubricants separate surfaces that are in motion (e.g., in rolling contact) at high relative speeds.
Compounds that serve well as boundary lubricants, which usually react and/or physically interact with surfaces, typically do not effectively lubricate surfaces that are in motion at high relative speeds. Conversely, elastohydroynamic lubricants provide a shear layer that separates and prevents contact between rolling surfaces. Elastohydrodynamic lubricants therefore do not serve as well at rest or at low relative speed conditions as do boundary lubricants. There are, however, systems containing contacting surfaces that require lubrication through a range of conditions, for example, from rest to high relative speeds.